Since I think the benefits of backwards compatibility is obvious to everyone on this site, i'll focus on why it might not be as good and idea.
Keep in mind though that, as a consumer, i would very much prefer my consoles backwards compatible, but these are just thought on why it might not be a big enough deal, to justify the added cost.
I'm gonna assume that it will make the consoles more expensive, to make them backwards compatible.
It's redundant.
Joe has a bunch of PS2 games lying around, but his PS3 is not backwards compatible. Yet Joe is not that sad about it.
How can he be so indifferent you might ask?
It's simple really, if he has the PS2 games, he most likely have the PS2 as well. Having the games, without the console is something very few people would have, (apart from situations where the console broke down ofc)
I don't use my wii for GC games, despite it beeing backwards compatible, because i have my trusty old GC for that.
Theres not really that big of a market for previous-gen games.
The game market is flooded with games. Games come out faster than most people can play them, if they strived to play them all.
I'd guess the people who wishes to seek out old gems, instead of getting a new game (or last years new game that has now dropped to a more costumer-friendly price) are a small minority.
I've heard many times before, that "core gamers" make up a minority of the market, catering to a minority within the minority, the group of core gamers who wish to replay a specific old game, might not be profitable bussiness, save for a few high-profile games, or previous installments in a series that spanned over console gens, god of war and metroid prime, for instance.
I'm well aware, that prev-gen games are re-released, and i've seen some people scorn it ála "I already bought god of war years ago, why the fuck should i pay for it again! rage rage rage"
Well you shouldn't then.
I don't think the re-releases of older games are meant to cater to the people who already own them.
I for one bought the god of war collection and the ico/SotC collection for my PS3, because i never had the chance to play those games on the PS2, because i didn't have one.
If they hadn't been re-released, and in a nice 2 for 1 pack, i probably wouldn't have gotten around to search for old PS2 copies, even if the PS3 had been backwards compatible.
Especially the god of war collection seems to me, to be catering more to the people who didn't play the first 2 games before, but who wants to catch up on the series before playing the 3'rd game.
If you already have them for your old system, and have played them already, why bother buying them again for the new system?
In the end, i don't really know if i'd be interested in paying a significant amount extra for backwards compatibility. Theres already coming more new games out that spark my interrest than i have time to play.
I actually find the current model, where they re-release classics and fan-favourites for the new consoles work just fine, because they let people who didn't play them on their original system get a chance at them, without costing the people who doesn't care any money, and i don't see why people who already own the original versions of the game, and their native consoles care.
Old consoels needs love as well, use them for their respective games.
Just some thought